LD5523D2

11/11/2020

13

Leadtrend Technology Corporation

www.leadtrend.com.tw

LD5523D2-DS-00 November 2020

OVP (Over Voltage Protection) on VCC

–

Auto Recovery

LD5523D2 is implemented with OVP function through

VCC. As the VCC voltage rises over the OVP threshold

voltage,

the

output

drive

circuit

will

be

shut

off

simultaneously thus to stop the switching of the power

MOS until the next UVLO (ON) arrives. The VCC OVP

function of LD5523D2 is an auto-recovery type. The Fig.

19 shows its auto recovery operation. That is, if the OVP

condition is removed, it will resume to normal output

voltage and VCC level in normal condition.

VCC

UVLO(on)

UVLO(off)

t

OVP Tripped

t

OUT

Switching

Switching

Non-Switching

OVP Level

Fig. 19

Over

Load

Protection

(OLP)

–

Auto

Recovery

LD5523D2 is implemented with OLP function. LD5523D2

features auto recovery function of it. In the example of the

fault condition, the feedback system will force the voltage

loop enter toward the saturation. As the built in VCOMP

tripped pull high level and stay for more than the OLP

delay time, the protection will be activated and then turn

off the gate output to stop the switching of power circuit.

The OLP delay time is set by internal high frequency

counter. It is to prevent the false triggering from the

power-on and turn-off transient. The OLP delay time is set

as 65ms without soft start.

FB Open/Short Circuit Protection

– Auto

Recovery for LD5523D2

In soft start period, the Fig. 20 shows the operation. When

FB lowers arm resistor is short to GND or upper arm

resistor open, which keeps on iFB smaller than 12.5

μA.

Then the soft start will turn to generate a driving signal and

keep auto recovery till FB open or short fault is removed.

The iFB current is a reflection voltage from primary side to

auxiliary winding through the FB upper arm resistor.

Fig. 20

Brown-In/ Brown-Out Protection (BNI/BNO)

– Auto Recovery

The

LD5523D2

integrates the

brown in,

brownout

protection and valley detection into FB pin. The auxiliary

voltage reflects a proportional bulk voltage during the on

time. Fix the internal current at the BNI, BNO and, the BNI

level could be set by modulating the FB divided resistors

and auxiliary voltage, as shown in Fig. 21. For preventing

the abnormal condition of line voltage to causing damage,

BNO function is implemented, while turns off the gate

signal after de-bounce time 75ms as BNO occurring, as

FB

FB Short

Level

t

FB Short

t

CS

Non-

Switching

Vcc

t

UVLO(on)

UVLO(off)

Soft Start

+

FB Short

Delay Time

OUT

t